Synthetic rubbers are commonly made by the anionic polymerization of conjugated diolefin monomers. For instance, polybutadiene rubber can be synthesized by initiating the polymerization of 1,3-butadiene monomer with an organolithium compound.
In some applications, it is critical for synthetic rubber to have a molecular weight which is within a specific range. The molecular weight of polymers synthesized by anionic polymerization is inversely proportional to the amount of initiator used. Thus, in cases where a low molecular weight is desired, a relatively large amount of initiator will typically be employed. However, the use of large amounts of initiator is expensive and greatly adds to the cost of producing polymers having extremely low molecular weights by anionic polymerization.
There is a need for a viable means to control the molecular weight of polymers made by anionic polymerization other than by adjustment of the initiator level. This invention relates to such a means for controlling molecular weight of polymers made by anionic polymerization.